1. Field
The following description relates to a method and apparatus to detect an intended packet by a sliding intermediate frequency (SIF) coherent ultra low power (ULP) wireless receiver.
2. Description of Related Art
The ultra low power (ULP) wireless communication has gained traction with the advent of Internet of Things (IoT), wearables and e-Health applications. In general, a ULP transceiver has low data rates, for example, 1 Mbps, and operates over short distances, for example, sub 50 meters (m). Existing ULP transceivers achieve power consumption of 1 nanojoule per bit (nJ/bit), which has led to the evolution of wireless communication standards like IEEE 802.15.4q and Bluetooth Low Energy (BLE).
A radio frequency integrated circuit (RFIC) is a dominant power consuming block in ULP wireless communication. In order to extract maximum power savings from the RFIC, ternary amplitude shift keying (TASK) has been developed as a baseband (BB) modulation technique in the IEEE 802.15.4q standard. TASK not only provides inherent modulation duty cycling at a transmitter power amplifier, but also leads to relaxed requirements on RFIC components, such as a frequency synthesizer and a phase locked loop (PLL).
IEEE 802.15.4q compliant ULP chipsets are expected to be deployed in e-Health and sensor applications, where the traffic is sparse and has a low duty cycle. However, the duration of noise interval preceding an IEEE 802.15.4q physical (PHY) layer packet may be quite long. Thus, it is important to design an energy detection (ED) processor configured to define or to provide a transition from a noise period to a signal period with high reliability. Further, the ULP chipsets operate in an unlicensed 2.4 gigahertz (GHz) industrial scientific medical (ISM) band, coexisting with wireless local area network (WLAN) devices, Bluetooth (BT), and Bluetooth Low Energy (BLE) devices. It is imperative to design a packet detection (PD) method that may reliably distinguish between IEEE 802.15.4q PHY packets and other PHY packets in the ISM band.
Carrier frequency offset (CFO) is a radio frequency (RF) impairment that arises due to a slight mismatch between a local oscillator (LO) at the ULP receiver and an LO at the transmitter. The CFO may lead to improper symbol demodulation and erroneous decisions in a bit decoding process. Hence, it is important to estimate a CFO and design a CFO compensation processor, even for low signal-to-noise ratio (SNR) regimes.
Automatic gain control (AGC) is a crucial feature of the ULP receivers to accommodate a wide dynamic range of received power levels. In absence of AGC, a total gain is fixed. This leads to either saturation effects or a low signal-to-noise ratio (SNR) at outputs of an analog-to-digital converter (ADC). In either case, a signal is not demodulated properly. Moreover, the performance of AGC may be affected by Direct current offset (DCO).
DCO is a problem in sliding intermediate frequency (SIF) ULP receivers when gains of BB stages are high. Even small magnitudes of DCO may be significantly amplified due to high gains.